What have you found to be the most "technically useful" iPhone app? I'm not talking about which Cabernet is the cheapest in the Chicagoland area, or a zipcode locator, etc.

i.e., I sail, so a wind speed meter, weather, chart and tide table would be useful apps. I work in the construction industry, so an engineering-calculator and clinometer/level would be useful tools. For both areas, a first-aid app might be useful as well. A plastics materials/process selection, or draft angle calculator app might be a good one for IDs.

Your thoughts?

Lew Morris"It's what you discover, after you know it all, that counts." _ John Wooden

Level (it is actually a level app. Not super accurate, but better than eyeing it)
Shazam (identifies songs playing wherever you are)
Skitch (allows you to annotate just about anything on the fly)
Autoblog
NBC (stream TV and news)
Uber (allows you to call a Lincoln Towne car to pick you up in most major cities, costs just a few bucks more than a cab in most cases and is great for getting to and from airports in busy cities)
LinkedIn (which acts as a nice contact book for me on the go)
Yelp
Open Table
iWant
moviefone